1. Field of the Invention
The present invention relates to a semiconductor memory device, a semiconductor device including the semiconductor memory device, and a method for detecting a defective memory cell in a memory device.
2. Description of the Related Art
In recent years, a metal oxide having semiconductor characteristics, which is called an oxide semiconductor, has attracted attention as a novel semiconductor material having high mobility as in the case of polysilicon or microcrystalline silicon and having uniform element characteristics as in the case of amorphous silicon. A metal oxide is used for various applications. For example, indium oxide is a well-known metal oxide and used as a material of a transparent electrode included in a liquid crystal display device or the like. Examples of such metal oxides having semiconductor characteristics include tungsten oxide, tin oxide, indium oxide, and zinc oxide. Transistors in each of which such a metal oxide having semiconductor characteristics is used for a channel formation region have been known (Patent Documents 1 and 2).